WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8653
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Article Citation - WoS: 1Scintillation Index in Non-Kolmogorov Jet Engine Exhaust Turbulence(IOP Publishing Ltd, 2026) Baykal, YahyaIn a non-Kolmogorov jet engine exhaust turbulence environment, scintillation index is found and evaluated. Effects of non-Kolmogorov turbulence spectrum, i.e., power law on the scintillations are studied. Variations of the scintillations against the change in the power law are found for various link lengths, structure constants, wave numbers, jet engine exhaust turbulence strengths, source sizes and scale parameters of jet engine exhaust turbulence. When the power law of non-Kolmogorov turbulence varies, the changes in the scintillations in jet engine exhaust turbulence are not large. The results in this paper could be of help to designers of optical wireless communication systems operating in atmosphere experiencing non-Kolmogorov jet engine exhaust turbulence.Article Transmittance of Gaussian Beam in Anisotropic Jet Engine Exhaust Turbulence(Pergamon-Elsevier Science Ltd, 2026) Baykal, YahyaTransmittance is a metric that provides information on how much of the intensity is transferred to the receiver for a given medium. One of the definitions of transmittance is the ratio of the average received intensity in the presence of turbulence to the received intensity in the absence of turbulence. Under such definition, transmittance is found in an anisotropic jet engine exhaust turbulent environment. For various receiver points, transmittances versus the wireless optical communication (WOC) link and anisotropic jet engine exhaust turbulence parameters are presented. The results are useful for designers of WOC links that are installed in the premises such as the airports that possess jet engine exhaust turbulence.Article Mitigation of Laser Beam Fluctuation and Performance of Probability of Fade in Weak Ocean Turbulence(Pergamon-Elsevier Science Ltd, 2026) Gercekcioglu, Hamza; Baykal, YahyaUtilizing the Rytov method in weakly turbulent oceanic medium, minimum scintillation index of sinusoidal Gaussian (SG) laser beams, named as the optimum beam (OB), is investigated for the underwater wireless optical communication (UWOC). Horizontal link between any underwater vehicles is considered. The formulation of the on-axis scintillation index of these beams is derived analytically, and the minimum scintillation index is determined with suitable adjustment of the complex displacement parameters. The complex displacement parameters are identified and tabulated for the selected propagation distance and source size. Obtained scintillation index results are drawn against the propagation length and source size. When compared with the plane, spherical, collimated, focused Gaussian, cos-Gaussian and cosh-Gaussian beams, OB is found to possess essential advantage. Additionally, with the obtained scintillation index values, probabilities of fade of these beams are calculated and their behaviors are also presented. OB also has a significant advantage when considering the fade probability.Article Scintillation Characteristics of Annular Beam Array in Underwater Optical Links(IOP Publishing Ltd, 2025) Erdogdu, Ekin; Gokce, Muhsin Caner; Baykal, YahyaUnderwater optical wireless communication systems offer a promising alternative to traditional acoustic methods for achieving high data rate transmission. However, the propagation of optical waves in underwater environments is severely impacted by oceanic turbulence, leading to intensity fluctuations and consequent performance degradation. In this work, we employ a laser beam array to model transmit spatial diversity for suppressing these fluctuations. The model uses annular-shaped lasers at the transmitter as a representation of beam shaping for turbulence mitigation, with a point detector assumed at the receiver. Through the use of the Huygens-Fresnel principle, we derive two key optical parameters: the average received intensity and the average of the intensity squared. We subsequently determine the scintillation index for this model. Our findings demonstrate reductions in scintillation under varying system parameters. For instance, increasing the number of beams in the array, the ring radius, and the secondary field amplitude of the annular beam leads to a lower scintillation index.Article Citation - WoS: 4Citation - Scopus: 4Transmittance of Gaussian Beams in Biological Tissues(Pergamon-elsevier Science Ltd, 2025) Ozcan, Murat Kaan; Gokce, Muhsin Caner; Baykal, YahyaThe study examines the average transmittance of Gaussian beams passing through various biological tissues, taking into account the impact of turbulence, absorption, and scattering. The extended Huygens-Fresnel technique, which utilizes the power spectrum of turbulent biological tissues, is applied to determine the optical intensity at the observation point. Additionally, there are tabulated absorption and scattering coefficients available for the application of the Beer-Lambert law, facilitating the calculation of optical light attenuation in biological tissues. Examining the impact of turbulence, as well as absorption and scattering-induced attenuation on the Gaussian beam's propagation, the changes in transmittance are documented across different tissue parameters.Article Citation - Scopus: 1Bit Segmentation of Non-Line of Sight Data in Optical Camera Communication Using U-Net(Iop Publishing Ltd, 2025) Ozkan, Cagla; Inan, Tolga; Baykal, YahyaOptical Camera Communication (OCC) utilizes image sensors to decode modulated light signals from light-emitting diodes (LEDs), offering a cost-effective solution for wireless communication. However, data extraction in non-line-of-sight (NLOS) conditions is challenging due to signal distortions caused by obstacles and reflections. Traditional segmentation techniques, such as Otsu's thresholding and adaptive thresholding, are computationally efficient but struggle with lighting variations, background interference, and high-frequency distortions, limiting their effectiveness in real-world OCC applications. To address these limitations, we propose a U-Net convolutional neural network, trained on a diverse dataset covering various camera distances, lighting conditions, and reflection levels to improve segmentation accuracy. The proposed model achieves up to 25% BER improvement, outperforming traditional thresholding methods and ensuring more reliable bit extraction in challenging OCC environments. These advancements make deep learning a promising approach for improving OCC applications such as indoor positioning, smart transportation, and secure optical wireless communication.Article Citation - WoS: 5Citation - Scopus: 6Bit Error Rate of M-Pulse Position Modulated Laser Beams for Vertical Links Operating in Weak Oceanic Turbulence(Iop Publishing Ltd, 2024) Gercekcioglu, Hamza; Baykal, YahyaThe on-axis scintillation index of laser beams is investigated by employing the Rytov method in a weakly turbulent oceanic medium for up/downlink coupling of laser communication between any underwater vehicles or divers. For vertical links, the formulation of the on-axis scintillation index of laser beams is derived analytically and evaluated for plane, collimated Gaussian and spherical beams in specific mediums, including the Atlantic Ocean at mid and low latitudes associating temperature and salinity changes at low latitudes, at mid latitude-summer and at mid latitude-winter. Using the scintillation index, bit error rate (BER) performance of M-pulse position modulation is investigated for these types of laser beams. The variations of the scintillation index against the uplink/downlink propagation distances, source size and zenith angle are examined, and BER variations versus the Kolmogorov microscale and the symbol orders, and results are compared. It is noted that the behavior of the scintillation index that depends on the relative strength of temperature and salinity fluctuations which changes in depth, is different for uplink/downlink and for each latitude due to its distinct characteristics. The source size that minimizes the scintillation index values is in the range of about 0.1 cm-0.2 cm for all latitudes.Article Citation - WoS: 4Citation - Scopus: 1Degradation of Signal-To Ratio Due To Turbulence in Various Biological Tissues(Iop Publishing Ltd, 2024) Baykal, YahyaWhen a biological tissue is excited by an optical beam, the presence of turbulence in the tissue causes the signal-to-noise ratio (SNR) to degrade. This degradation is in reference to the SNR value in the absence of tissue turbulence. The effect of tissue turbulence in reducing the SNR is examined. SNR reductions are examined for various types of biological tissues such as liver parenchyma (mouse), intestinal epithelium (mouse), upper dermis (human). Also, SNR reductions in the turbulent tissue are evaluated against the changes in the strength coefficient of the refractive-index fluctuations, fractal dimension, characteristic length of heterogeneity, small length-scale factor, tissue length, wavelength and the source size.Article Citation - WoS: 1Citation - Scopus: 2Scintillation Index and Outage Probability of Vortex Gaussian Beams for Horizontal Links in Weak Atmospheric Turbulence(Iop Publishing Ltd, 2024) Gercekcioglu, Hamza; Baykal, YahyaUsing the Rytov method, the off-axis scintillation index for a Gaussian vortex beam is examined in horizontal laser communication links operating in a weakly turbulent atmosphere. The performance of laser communication systems, defined in this study by the outage probability, is evaluated using the lognormal distributed intensity to find the scintillation index. The off-axis scintillation index of vortex Gaussian beams is analytically derived and evaluated in horizontal atmospheric links. The scintillation index obtained from the figures drawn versus the source size and propagation length is used to calculate the outage probability. It is found that turbulence affects vortex Gaussian beams less than non-vortex Gaussian beams. Our important finding is that the scintillation index is reduced when the topological charge increases.Article Citation - WoS: 3Citation - Scopus: 4Adaptive Optics Compensation of M-Ary Pulse Position Modulated Communication Systems in Anisotropic Non-Kolmogorov Turbulent Atmosphere(Elsevier, 2021) Ata, Yalcin; Baykal, Yahya; Gokce, Muhsin CanerAdaptive optics compensation effect on the performance of an optical wireless communication system (OWC) employing M-ary pulse position modulation (PPM) scheme in anisotropic non-Kolmogorov turbulent atmosphere is investigated. Avalanche photodetector (APD) is used at the receiver side and log-normal channel that models the weak turbulence conditions is utilized. Anisotropy, generally resulting in better performance in OWC systems operating in the turbulent medium, combined with the adaptive optics applications will enhance the bit-error-rate (BER) of the OWC systems significantly. Results are obtained depending on various parameters for both the turbulent atmosphere and the receiver. Our work gives OWC system designers a perspective to optimize their design.